Magnetic core transformer with an adjustable coupling factor



April 15, 1969 MAGNETIC CORE TRANSFORMER WITH AN ADJUSTABLE COUPLINGFACTOR Filed April 20, 1966 s. SCHWEIZERHOFY Sheet 014 l l/ I i [0 HSIGNAL. W APPLYING 1 9. l MEA NS 1 I le "11 OUTPUT SIGNAL 21V SIGNALAPPLYING /22 MEANS MEANS 6 l I I J l i k 1 Pl Ic 7: a l, 4, F/g. 2

INVENTOR Sigfrid Schweizerhof ATTORNEYS April 15, 1969 s. SCHWEIZERHOF'3,439,257 MAGNETIC CORE TRANSFORMER WITH [KN-ADJUSTABLE COUPLIN G FACTORFiled April 20. 1966 Sheet 2' 014 Fig. 4

mvsrvron Sigfrid Schweizerhof AT'TORN EYS April v 15, 1969 I s.SCHWEIZERHOF MAGNETIC CORE TRANSFORMER WITH AN ADJUSTABLE COUPLINGFACTOR Filed April 20, 1966 Sheet ATTORNEYS Filed April 1 20. 1966 w v.v w- V7(MV) s. SCHWEIZE RHOF 3,439,257 MA GNET IC LCORE TRANSFORMER WITHAN ADJUSTABLE COUPLING FACTOR Sheet 4 of 4 e; (A MPE RE -TUHV$) Fig.6

INVENTOR Sigfrid Schweizerhof ATTORNFYS us. Cl. 323-56 United StatesPatent 3,439,257 MAGNETIC CORE TRANSFORMER WITH AN ADJUSTABLE COUPLINGFACTOR Sigfrid Schweizerhof, Backnang, Germany, assignor to TelefunkenPatentverwertungsgellschaft m.b.H., Ulm (Danube), Germany Filed Apr. 20,1966, Ser. No. 543,926 Claims priority, appliction Germany, Apr. 22,1965,

Int. Cl. H02p 13712; H02m 5/12 Claims ABSTRACT OF THE DISCLOSURE Amagnetic core transformer, having an adjustable coupling factor whichcan be varied by means of a control current. The transformer has amagnetic core having four core zones made of the same material andarranged between four apertures. The core zones and the apertures aresymmetrically arranged with respect to the center of the magnetic core.Also included in the transformer are an input and output winding, eachpenetrating two apertures which lie on diametrically opposite sides ofthe magnetic core center, and a control means for selectivelymagnetizing, up to saturation, two of the core zones that lie ondiametrically opopsite sides of the core center. The control meansincludes a control winding and means for passing an adjustable controlcurrent through the control winding, so that in the absence of controlcurrent, there will be no inductive coupling between the input andoutput windings and as the control current is increased, the inductivecoupling will increase.

The present invention relates to magnetic core transformers and to suchtransformers having a variable coupling factor which can beelectronically regulated.

More particularly, the invention relates to magnetic core transformerswherein the coupling factor may be electronically regulated over a widerange by current means such as a control current, an adjustable directcurrent or current pulses, and such transformers have many uses,particularly in the communication art. For example, such transformersmay be used for quickly establishing electrical connection in gatecircuits for alternating currents or pulse signals. Also, this type oftransformermay be used in electronic telephone exchange systems fortesting the coil and busy condition of the subscriber lines and whereinthe line current to be detected flows through the control coil of thetransformer, causing the test signal which is electrically separatetherefrom to be switched through the output of the transformer. The testsignal may be in the form of a continuous alternating voltage or of avoltage pulse. The afore-described magnetic core transformers may alsoserve as modulators whereby the modulation of the input voltage iseffected by varying the coupling between the input winding and theoutput winding. Furthermore, trans-formers having a coupling coefficientwhich can be electrically regulated may also be used as magneticamplifiers if such transformers have a coupling factor which can beregulated within desired limits and with relatively low control power.

In the majority of applications for such magnetic core transformers, twofactors are of primary concern. Thus, not only is the greatest possiblevariation in the coupling factor desirable, but above all, it isdesirable to provide the transformer with complete decoupling betweenthe input and output winding while maintaining adequate decouplingbetween these windings and the control winding.

Although prior art arrangements have attempted to provide each of thesefeatures in a single magnetic core transformer arrangement, it haspreviously been found that with the prior art arrangements only onedesirable feature can be maintained at one time.

The prior art proposals include arrangements in which the degree ofcoupling between two coils is varied within certain limits by adjustingthe permeability of the coupling ferromagnetic core through means of aseparate bias magnetization winding arrangement as a result of which,the leakage inductance of the two windings is varied at the same time.These arrangements, however, have the decisive disadvantage for manyuses in that a complete coupling and above all a complete decouplingbetween the input winding and the output winding is not obtainable, evenwith the aid of very large control fluxes. In addition, thesearrangements also suffer from an undesirably large variation in theinductance of the transformer windings.

There have also been provided magnetic amplitude modulator arrangementsin which the carrier signal is modulated by means of direct currentbias-magnetized controllable inductors such as are shown in GermanPatent No. 1,050,839. However, the blocking to passing ratio of suchinductors, which depend on the shape of the magnetization curve of thecore material, is not very satisfactory and moreover, such arrangementsgenerally necessitate the use of additional transformers.

Other arrangements are also known in which complex circuits havingcurrent-controlled inductors serve for precise modulation or signaltransmission. Such an arrangement is disclosed in German Patent No.910,671. However, the inductors only operate with resonant tuning andcan therefore only be used for a specific carrier frequency and, inaddition, a considerable expenditure for the arrangement is required dueto the complex circuitry therefor.

Another known arrangement includes the use of superconducting materials.In this arrangement the coupling between two adjacent coils is varied insuch a manner that an interposed plate is driven, by means of acontrollable magnetic field, out of the superconducting state, i.e.,complete magnetic shielding, into the normal conducting state, i.e.,weak shielding. This method, however, has the disadvantage that itrequires a complex and expensive lowtemperature cooling arrangementwhich uses, for example, liquid helium as the refrigerant, andfurthermore, this method presents practical difliculties because of thevery narrow transistion region between the two states of conductivitysuch that the desired coupling effect can not always be achieved.

It is therefore a primary object of the present invention to provide amagnetic core transformer which overcomes the disadvantages of prior artarrangements.

It is another object of the present invention to provide a magnetic coretransformer having a coupling factor which can be regulated over a widerange.

It is a further object of the present invention to provide a magneticcore transformer which also provides for complete decoupling between theinput and output windings while maintaining adequate decoupling betweenthese windings and the control windings.

In essence, the objects of the present invention are achieved byproviding a transformer having a core with four symmetrically arrangedapertures wherein each of the input and output windings penetratesthrough two different non-adjacent apertures of the core. Thearrangement is such that when the input winding is energized, theassociated total magnetic flux provided thereby does not permeate thetotal turn area of the output winding and thereby provides zerocoupling. A control winding is passed through all four apertures in sucha direction that two non-adjacent of the four core zones, hereinafterreferred to as control webs, situated between the apertures can besaturated by the control flux such that by means of a control current,the closed flux path of the input winding, to an adjustable extent, canbe caused to pass through the turn area of the output winding forproviding a coupling factor other than zero.

Additional objects and advantages of the present invention will becomeapparent upon consideration of the following description when taken inconjunction with the accompanying drawings in which:

FIGURE 1 is a simplified pictorial view of a magnetic core transformerarrangement according to the present invention.

FIGURE 2 is a simplified pictorial view of another embodiment of atransformer arrangement according to the present invention.

FIGURE 3 is a side view of a further transformer embodiment according tothe present invention in which the core is formed from a plurality ofpieces and the coils are shown in cross section.

FIGURE 4 is a plan view, partly in cross section, of the transformerarrangement of FIGURE 3.

FIGURE '5 is an exploded perspective view of a transformer arrangementincluding two disc-shaped cores as shown in FIGURE 1.

FIGURE 6 illustrates a curve of the output voltage versus control fluxfor the arrangement of FIGURE 5.

Referring now to the drawings, there is shown in FIGURE 1 a transformerarrangement including a disclike core 1 having four circular apertures2, 3, 4 and 5 respectively, with the centers of such apertures beingarranged in the form of a rhombus in the plane of the core so thatimaginary lines drawn between these centers would be perpendicular toone another and bisect one another to form a square. An input winding 6having a signal applying means 20 connected thereto is arranged to passthrough the core 1 by passing through the apertures 2 and 4, thussurrounding the middle part of the core. An output winding 7 which is tobe coupled to the input Winding also passes through the core by passingthrough apertures 3 and 5 and forms a further winding about the centerpart of the core which is perpendicular to the input winding 6, theoutput winding having a signal receiving means 21 connected thereto. Acontrol winding 8 which comprises two component windings 9 and 10connected in series passes through all four apertures in the core andhas a signal applying means 22 coupled thereto such that when a signal,for example, a variable direct current I is passed through the windingin the direction shown in the drawing, the control winding effects achange in the coupling factor. Due to the apertures, the core is formedwith four core webs which separate the apertures and two of such websare surrounded by the control winding and are shown hatched in thedrawings. These webs are designated as control webs and are magneticallysaturated to varying degrees by the control winding at their narrowestpoint:

It is readily apparent from the arrangement illustrated in FIGURE 1 thatwithout the bias magnetization provided by the control current, i.e., I=0, the magnetic coupling between the input winding 6 and the outputwinding 7 will be zero for reasons of symmetry. However, the passing ofa control current through the control winding causes the control webs tosaturate and thus there will be provided a corresponding increase in themagnetic resistance, with the flux produced by the input winding 6,shown in broken lines in FIGURE 1, spreading to an increasing extent tothe other webs of the core which are not saturated and result in thepermeation of the turn area of the output winding 7. On completesaturation of the control Webs, the magnetic coupling between the inputwinding and the output winding substantially obtains the full couplingvalue of unity.

Although the core is shown as being disc-shaped in FIGURE 1 the core isnot limited to such shape and may differ to a large extent therefrom.For example, as shown in FIGURE 2, although there is again provided adiscshaped core 1, the apertures 2' to 5' therefore are provided with asector-like shape which is more favorable for the blocking of thecontrol webs by saturation. In this figure, the input and outputwindings and also the control windings correspond to those windingsshown in FIGURE 1.

The core may also be produced from a plurality of parts in the interestof more simple production methods and winding techniques for thetransformer and particularly for the purpose of using prewound coilswhich can be slipped onto the core. The core parts may be assembled, forexample, with highly machined joints or in the form of an overlappedstacking of transformer laminations. Such a core is illustrated inFIGURES 3 and 4, in which FIGURE 3 is a side view and FIGURE 4 a topview thereof. As shown, the core 1 is in the shape of a square andcomprises four component cores 1a, 1b, 1c and 1d which bear against oneanother at their highly machined surfaces. The two inner component cores1b, and 1c, are constructed in the form of E-cores and the outercomponent cores 1:: and 1d in the form of U-cores. The finished windingswhich are wound on coil formers are mounted in the four apertures 2",3", 4" and 5". The assembly of this transformer is effected by insertingthe E-cores 1b and 1c laterally into the coil formers carrying theoutput winding 7 and the control winding component 9. Then, the coilformer carrying the input winding 6 and the control winding component 10is slid over these E- cores from above or from below, with the U-cores1a and 1d being pushed laterally over the latter coil formers and theE-cores to complete the transformer assembly.

It is apparent from FIGURES 3 and 4 that the two component windings 9and '10 which are connected in series to form the control winding 8 arearranged in different core apertures than that shown in FIGURES l and 2.However, the direction of the current in these component windings whenpenetrating the various apertures is such that the effect of the controlwindings on the input and output windings is the same in both cases.

In FIGURE 5 there is shown a further embodiment of the present inventionfor eliminating an undesired coupling which still exists between thecontrol circuit and the transformer circuit in the arrangement of FIG-URE 1. As shown in FIGURE 5, there are provided two similar transformerassemblies as shown in FIGURE 1. These two assemblies are combined suchthat the voltages induced by the coupling of the transformer circuitsand the control winding and vice versa, are compensated for, forexample, by a series connection in opposition of the two controlwindings. Thus, two transformer cores 1 are arranged to lie closely oneabove the other, however, these cores are shown separated in an explodedview for reasons of clarity. The input winding 6 and output winding 7are passed jointly about the two cores with these connections beingshown by lettered connection points A to E for the sake of clarity.However, each core 1 is provided with a separate control winding similarto that shown in FIGURE 1. Therefore, the control winding 8 is providedwith four components 9, 10, 11 and 12, the components 9 and 10 beingwound in series about the control webs on the top core and connected atthe point G to the components 11 and 12 which are wound in seriesopposition to the components 9 and 10. Accordingly, with thisarrangement, the coupling between the transformer circuits and thecontrol winding is eliminated.

The two cores shown in FIGURE 5 may, for example, be made from highlypermeable ferrite plates having the following dimensions: an outsidediameter of 45 mm., a thickness of 3 mm., an aperture diameter of 11mm., and

a minimum control web width of 2 mm. The transformer input and outputwindings 6 and 7 each may comprise fifteen turns which are wound jointlyover both cores with the control winding 8 comprising four componentwindings of fifty turns each which are wound separately over both cores.

In FIGURE 6, there is shown a curve representative of the output voltageV and its dependency on the number of ampere-turns for the controllabletransformer of FIGURE having the above-mentioned dimensions. It shouldbe noted that these dimensions are only illustrative and although atransformer constructed according thereto effects the desired decouplingbetween the control and transformer windings so as to satisfy theobjects of this invention, these dimensions are not necessarily optimum.The measurements were taken with the transformer having a transmissionratio of 1:1 at a frequency of 100 kc.p.s. and with a loading of 150ohms. As shown, FIG- URE 6 indicates a considerable variation in theoutput voltage V, which rises from very low values to essentially thefull value of the input voltage V with an increase in the control numberof ampere-turns 0,, The approximation to a zero output voltage in thedecoupled state is, in practice, only limited by the asymmetries in theposition of the core apertures and by the capacitative coupling betweenthe transmitter windings. These factors, however, do not effect theprinciple of the present invention and the influence thereof can bereduced to a very great extent.

Thus, it is apparent from the above description that the magnetic coretransformer according to the present invention not only provides acoupling factor which can be electronically regulated over a wide range,but above all, provides an essentially complete decoupling between theinput and output windings and an adequate decoupling between thesewindings and the control winding. Accordingly, the magnetic coretransformer according to the present invention has a great number ofuses. For example, the transformer may be used for establishingconnections through gate circuits and may also be used to advantage foramplitude modulation, for magnetic amplification and for measuringcircuits. For providing an amplitude modulated signal, the signalapplying means 22 applies a verying control signal to the controlwinding such that the input signal applied by means 20 would result inan amplitude modulated signal. In the case of a magnetic amplifier, acontrol signal for providing the desired amplification factor isapplied. For use as a measuring circuit, a signal to be detected isapplied to the control winding, such that given a predetermined inputsignal, the resultant output signal is indicative of the detectedsignal. It should also be noted that its use is not restricted toalternating current signals and that the transformer can be used forsignals to be transmitted in pulse form and/ or control signals in theform of pulses.

The relationship between the coupling factor and the control currentdepends on the magnetization curve of the core material and on themagnitude and the crosssectional configuration along the control webs,and is therefore generally non-linear. In the case of transformers forswitched through connections this provides no disadvantages sinceherein, it is only important to provide a sharp rise in the couplingwith the control current. This rise can easily be achieved by means of acore material with a steep hysteresis loop and small remanence andcoercive field strength and also by means of control webs having a smallenough cross section so as to just permit the alternating current orpulse power to be transmitted. If the device is to be used formodulation purposes, the relationship between the control flux and thecoupling factor may be made linear to a certain extent or it may beapproximated to another desired function by the selection of a suitablecore material and by appropriate shape of the control webs between theapertures. Furthermore, the operating point of the modulator may befavorably adjusted by means of additional bias magnetization.

As previously discussed, the core for the transformer may have differentshapes and may be formed differently. For example, depending upon thefrequency level to be transnntted or the shape of the pulses to betransmitted, the magnitude of the available control power and otherconditions for a particular use of such transformer, the core mayconsist of a stack of transformer laminations or may be produced fromsoft magnetic ferrite materials. Ferrites with low saturation inductionand high permeabil1ty are particularly advantageous when control powerhas to be very low with a low power to be transmitted, for example, inmodulators or magnetic amplifiers. Furthermore, ferrites permit thetransmission or modulation of high frequencies. Therefore, thetransformer structure greatly depends upon the application for suchtransformer.

It will be understood that the above description of the presentinvention is susceptible to various changes, modifications, andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

What is claimed is:

1. A magnetic core transformer having an adjustable coupling factorwhich can be varied by means of a control current, said transformercomprising, in combination:

(a) a magnetic core having four core zones made of the same material andarranged between four apertures, said core zones and said aperturesbeing symmetrically arranged with respect to the center of said magneticcore;

(b) an input winding penetrating through two of said four apertureswhich are arranged on diametrically opposite sides of said center;

(c) an output winding penetrating through the other two of said fourapertures which are arranged on diametrically opposite sides of saidcenter;

((1) control means for selectively magnetizing, up to saturation, two ofsaid core zones which are arranged on diametrically opposite sides ofsaid center, said control means including a control winding throughwhich may be passed a control current, whereby, in the absence of saidcontrol current, there is no inductive coupling between said input andsaid output winding and, as said control current is increased, saidinductive coupling increases.

2. The transformer defined in claim 1, wherein said magnetic core isentirely made of the same material.

3. A transformer as defined in claim 1 for providing high controlsensitivity wherein the narrowest cross section of said two core zonessituated between said apertures is sufficiently large for the maximumpower to be transmitted.

4. A transformer as defined in claim 1 wherein the configuration of thecross section of said two core zones provides a desired relationshipbetween the degree of coupling and the control current, theconfiguration depending upon the shape of the magnetization curve for 1the core and upon the transformer uses.

5. A transformer as defined in claim 1 wherein for transmitting lowpowers with a high control sensitivity said core comprises highlypermeable materials having a low saturation induction.

6. A transformer arrangement as defined in claim 1 and furthercomprising another of said transformers, said transformers beingconnected together for compensating for the voltages induced by couplingbetween the control windings and the input and output windings of thetransformer arrangement.

7. A transformer arrangement as defined in claim 6 wherein the cores aremounted in a superposed relation and the input and output windings eachpass jointly about each of the cores forming the transformer arrangementand the control winding is wound separately on each of said cores.

8. A transformer arrangement as defined in claim 7 wherein said controlwinding comprises four component windings, each of said componentwindings being wound about a respective one of said two core zones ineach core with two of said component windings on one of said cores beingwound in series opposition to the other two of said component windingson said other core.

9. In combination with the transformer as defined in claim 1, means forapplying a signal to said input winding, and means for applying avarying control signal to said control winding for providing anamplitude modulated signal at said output winding such that saidtransformer serves as an amplitude modulator.

10. In combination with the transformer as defined in claim 1, a circuitarrangement including means for applying a signal to said input windingand means for applying a signal to be detected to said control windingfor providing an output signal at said output winding such that saidtransformer serves as a measuring circuit.

8 V References Cited UNITED STATES PATENTS 7/1948 McCreary 321-6811/1948 McCreary 321-68 2/1949 McCreary 32168 12/1952 McCreary 323-453/1953 Howlett 336212 X 3/1955 McCreary 332--51 8/1957 Dewitz 3361714/1960 Cornell 336-212 FOREIGN PATENTS 4/1958 France.

WARREN E. RAY, Primary Examiner.

US. Cl. X.R.

